This invention relates to a compound steel oil ring assembly and, more particularly, to improvements in a compound steel oil ring assembly having a spacer expander and side rails disposed above and below the spacer expander and brought into pressured contact with the inner wall of the cylinder of an internal combustion engine by the spacer expander.
In a conventional compound oil ring assembly, a situation arises in which the side rails disposed above and below the spacer expander undergo rotational motion in the circumferential direction during operation of an internal combustion engine, as a result of which the openings in the upper and lower side rails become aligned one above the other. In such case, a thick lubricating oil film formed by the gaps in the openings of the side rails is left on the cylinder wall in the form of streaks, and the oil is carried into the combustion chamber of the internal combustion engine. Such oil is consumed wastefully.
In order to solve this problem, the applicant has previously proposed a compound steel oil ring assembly having side rails the inner circumferential surfaces of which are formed to have fine corrugations extending in the axial direction (see Japanese Utility Model application Laid Open No. 1-78769).
However, a desirable method of forming the corrugations disclosed in the above-mentioned publication has not been developed, and manufacture continues to be performed by a manual operation.